Overload safety device for material handling mechanism



Aug. 10, 1965 c. w. BOPP 3,199,685

OVERLOAD SAFETY DEVICE FOR MATERIAL HANDLING MECHANISM Filed March 2, 1964 2, Sheets-Sheet 1 F113. 5. r --1 r r i 1 35b 38 I 350 I380: 38b Off Off I I 36 |I Up Down: {Dawn (Up :00! In -2 .J 1 1 INVENTOR. cEc/L n. BOPP MP, ,4 MW/ A fforneys C. W. BOPP Aug. 10, 1965 OVERLOAD SAFETY DEVICE FOR MATERIAL HANDLING MECHANISM Filed March 2, 1964 2 Sheets-Sheet 2 l/VVEN TOR. CECIL n. BOPP A f forneys United States Patent Filed Mar. 2, 1964, Ser. No. 348,593 8 Claims. (Cl. 212-39) This invention relates to an improvement in safety devices for detecting an overload condition in a material handling mechanism, and more particularly to a device for automatically limiting deflection in a stressed member of a material handling mechanism.

A contemplated use of the invention is with a material handling mechanism having two stressed main members, a vertical mast and a horizontal boom from which a load is suspended, and means for a plurality of movements of said load.

When a load is handled, a small but detectable amount of deflection occurs in the support members, and, within known or calculable limits, the stressed member will return to its original configuration when the load is removed. Since this deflection is proportional to the load applied, it may be used to generate a response to an approaching overload condition.

Means for detecting overloads in material handling mechanism are not new. However, prior devices do not sense an actual deflection in a stressed member, and the actuation of said devices may give only a visual and/or audible indication to an operator who must then respond to the indication. Such devices as are automatic completely stop all mo ements without provision for operations which would tend to alleviate the overload condition.

The present invention not only detects an approaching overload condition by sensing deflection in a stressed member, but automatically interrupts circuitry controling the means causing deflection-increasing movement of a load, while at the same time permitting actuation of means for deflection-decreasing movements. Thus, the dangers inherent in operator inattentiveness and improper operator response to a mere visual and/ or audible indication is considerably lessensed.

An important object of my invention is to provide a means for directly sensing an actual deflection in a stressed member of a material handling mechanism and to provide means for automatically limiting said deflection to a safe amount, while at the same time permitting corrective operations.

Another object of my invention is to provide a device for limiting deflection which can be suitably mounted on a stressed member of a material handling mechanism.

Another object is to provide a means for adjusting and pro-selecting the amount of deflection necessary to actuate the device and for compensating for other variables, such as mounting position.

These and other objects of my invention may be more fully understood by reference to the accompanying drawings, in which:

FIG. 1 schematically illustrates a side View of a form of material handling mechanism with the device selectively mounted on the mechanism boom or mast members;

FIG. 2 is a plan view of the device (top cover removed) mounted on a boom member;

FIG. 3 is a side elevation of the device (side cover removed);

FIG. 4- is an electrical schematic of the microswitches and associated control circuitry employed with the device; and

FIG. 5 is an electrical schematic of an alternate con trol circuit.

Construction Referring to the drawings and first to FIG. 1, a preferred form of the device 2 is shown mounted on a typi cal material handling mechanism 3 having two stressed members, a mast 4 and a boom 5. The device 2 is shown mounted on the top of boom 5, it being understood that it could be mounted on the mast 4 as indicated by the device 2a. The material handling mechanism 3 has means for a plurality of movements of a load 6 suspended from the boom 5. i

The arrowheads 7, 8, 9, iii, 11, 12 indicate typical movements of the load 6. Arrowheads 7 and 8 indicate reciprocate vertical movement; arrowheads 9 and iii indicate longitudinal movement; arrowheads 11 and 12 indicate movement in elevation. It is apparent that movements in the direction of arrowheads S, 9 and 11 will increase deflection in boom 5 and mast 4, these being termed forward movements, whereas movements in the direction of arrowheads 7, It and 12 will decrease deflection, these being termed reverse movements.

Referring now to FIGS. 2 and 3, the device 2 is shown mounted on a boom 5 with an environmental cover 13 of light sheet metal construction detachably mounted to boom 5 to permit removal of the cover for adjustment of set screws 14, 15 and i6 and bolt 17 and having an aperture in one side to accommodate socket i8 and associated wiring.

The lever arm mounts 19 of rigid metal construction are welded to boom 5 and are parallel to each other at a distance such as to accommodate lever arm 20 between them.

The lever arm 26 is a rigid member of suitable form which is illustrated as a square tubular member, bifurcated at one end to accommodate switch bracket 21 and an aperture in the top face to accommodate screw threaded bolt 17 and apertures at the bifurcated end to accommodate bolt 22. The opposite end of thee lever arm 29 is welded to the two lever arm mounts 19 so that the lever arm 26 is disposed in fixed spaced longitudinal relation to the boom.

The switch bracket 21 is of generally U-shape and positioned so that the open end of the U faces the boom 5, and is bifurcated at both ends, having suitable apertures in both sides thereof to accommodate bushing 23, bolt 22 and switch bolts 24. A brace plate 25 is welded to and connects the confronting sides of the bifurcated end nearest the lever arm mounts 19, which brace plate 25 has an aperture therein for reception of bolt H7.

The switch bracket 21 is disposed within the bifurcated end of lever arm 2t and is pivotally connected intermediate its ends to the lever arm 2t) by means of bushing 23 and bolt 22, and is adjustably connected at its inner end to the lever arm 26 by means of bolt 17 and spring as emplaced around said bolt and between the brace 25 and lever arm 21 to bias its pivotal movement relative to lever arm 26 and adjusting bracket 31. This spring-biased connection permits the microswitches to yield to prevent the crushing of the microswitches should the deflection exceed the overtravel of the microswitch contacts.

Inner spacers 27 are concentric with bolt 22 and bushing 23 and are positioned between the switch bracket 21 and lever arm 20 to prevent lateral movement of switch bracket 21 in order to keep microswitches 28, 29 and 3t? properly positioned beneath set screws 14, 15 and 16.

The microswitches 28, 29 and 3d are of .a standard type, well known to the art, and are mounted side-by-side in the same plane, joined together by bolts 24; microswitch 29 being partially enclosed by switch bracket 21, but sufliplate ciently exposing its contacts to permit operation by set screw 15. Said microswitches 28, 29 and 30 being electrically connected with the means for movement of a load.

Adjusting bracket 51 is of a metal construction and shaped so as to provide two spaced side walls and a rectangular top wall. Suitable threaded apertures in the top wall accommodate set screws 14, 15 and 16 and a large aperture in one side Wall receives a socket 18 secured in place by any suitable means such as screws. The bracket 31 may be secured, as by welding, in fixed relation to boom 5 and positioned such that the set screws 14, i5 and 16 are vertically disposed over the contacts of microswitches 23, 2? and 3t).

Referring now to FIG. 4, a typical control circuit is schematically illustrated to set forth the relation of the microswitch members to the operation of the mechanism 3. The control circuits otherwise form no part of the present invention. The dotted lines and legends serve to distinguish the circuitry associated with particular movements of the load 6. The circuitry indicated generally as 33 controls the reciprocate vertical movements of the load 6, i.e., the hoist control. This circuitry comprises two parallel branches, in one branch is a motor coil 33 for lowering the load 6; in the other branch is microswitch 29 in series with motor coil 35 for raising the load 6. Switch 37 is a single polo double throw switch having two contacts 37a and 37b for mutually exclusive connection to either of said branches. Switch 34 is a single pole single throw on-ofl switch in series with switch 37.

Boom control circuitry is indicated generally as 33a and controls movements in elevation. There are two parallel branches, one branch comprising motor coil 32% for raising the boom, the other branch comprising microswitch in series with motor coil 35a for lowering the boom. Switch 370 is a single pole double throw switch having two contacts 37d and 3% for mutually exclusive connection to either of said branches. Single pole single throw on-off switch 34a is in series with switch 37c.

The circuitry indicated generally as 33b controls the trolley travel, i.e., movements of the load 6 longitudinally of the boom 5. There are two parallel branches, one branch comprising motor coil 34% for movements inward toward mast 4, the other branch comprising microswitch 39 in series with motor coil 35b for outward movements away from mast 4-. Single pole double throw switch 37; has contacts 37g :and 3711 for mutually exclusive connection to either of said branches. Single pole single throw switch 34!) is in series with switch 37 The circuits 33, 33a and 33b are all in parallel with power supply as.

Referring now to FIG. 5 wherein an alternate control circuit arrangement is shown. Hoist motor coils 35 and 58 are in parallel and actuate up and down movements, 'espectively. Switch 42 is a three position stepping switch or the like having an OFF position and two other positions for mutually exclusive connection to either coil 35 or 38. Boom motor coils 35a and 38a and switch 42a. are arranged in an identical manner as are trolley motor coils 35b and 38b and switch 421'). The aforementioned coils and switches together form a parallel combination in series with a second parallel combination comprising microswitch 29a in parallel with override switch 43. The power supply 36 is in series with these two parallel combinations.

Operation Referring now to FIG. 4, as Well as to FIGS. 1, 2 and 3, assume that a force is stressing boom 5 as a result of lifting or attempting to lift load 6 suspended from boom 5 by means of a hoisting mechanism controlled by the circuitry 33 of FIG. 4. On this assumption a complete circuit exists through switch 34, switch 37 in position 37a, the normally closed microswitch 29, up coil 35 and power supply 36.

When the load exceeds the limits preselected by adjusting set screw 15 and bolt 17, an excessive deflection will occur in boom 5. Since greater deflection occurs at the position where the adjusting bracket 31 is located, rather than at the end where the lever arm 29 is mounted, the deflection brings set screw 15 in contact with microswitch 29 by the relative movement of adjusting bracket 31 with respect to switch bracket 21, opening the normally closed contacts of microswitch 29, thus automatically interrupting the circuit of the hoisting motor coil 35', and maintaining this de-energized state so long as the deflection exceeds the preselec ed limits. When the aforementioned condition exists, the only operator action the circuitry allows is one which will lessen the deflection on the boom 5, thus the operator may position switch 37 in its alternate position 37 b, thus forming a complete circuit with the power supply 36, switch 34, switch 3'7 in position 37b and down coil 38. When corrective action has succeeded in decreasing deflection to a safe level, the microswitch 29 will again close, thus enabling normal operations as selected by the operator. The circuits 33a and 53b operate in substantially similar fashion.

It is understood that all microswitches open simultaneously, thus disabling all forward or deflection-increasing movements of the load. Likewise, ail circuits for movement in the reverse or deflection-decreasing directions remain enabled when the microswitches are open.

Referring now to FIG. 5 wherein an alternate circuit arrangement is shown which may be used to accomplish the same result with the use of out one microswitch.

Upon deflection of boom 5 for any reason, the normally closed contacts of microswitch 2% will open to simultaneously interrupt power to all coils. The override switch 43 is normally open and, being in parallel with the microswitc'n 29a and also in series with the parallel combination mentioned earlier, the operator may bypass the microswitch, and by properiy positioning switches 42, and Mia, selectively operate any movement of the load, including forward movements if necessa y or desirable.

It should be understood that other control circuit arrangements may be used within the scope of my invention, and that the control circuitry other than the microswitches is ph sically remote from the device 2, any other switches usually being operated from a control console or portable control box or the like.

Mounting of the safety device may be on either a vertical or horizontal support member. Variances in the mounting position may be compensated for by proper adjustment of the safety device as hereinafter described.

Coarse adjustment may be accomplished by adjusting bolt 17, causing the pivotally mounted switch bracket 21 to move in relation to the lever arm 25 and adjusting bracket 31 and set screws 14, 15 and To, thereby changing the distance between the contacts of microswitches 28, 29 and 3d and the set screws 14, t5 and in. The proper adjustment can be made by preparing a load to be lifted, which load is to be the maximum load desired, and by so positioning the set screws 14, 15 and 16, that a greater load than the maximum desired will cause a deflection suflicient to open the microswitch contacts. This is but an example since the method of adjusting will be obvious to those skilled in the art, and it should be understood that a few simple trial and error adjustments will normally be required.

These and other advantages will be apparent to those skilled in the art. It will be understood that various changes and modifications may be made in the construction and arrangement of parts within the scope of my invention. For example, the drawings shown illustrate a device to be mounted in the same plane as the force producing the deflection and on that side of the stressed member which is under a tension as opposed to a compression (rear or top mount), Whereas by re-orienting and modifying certain parts, the same device may be mounted in a plane perpendicular to the force producing the deflection (side mount).

I claim:

1. In a material handling apparatus of the type described having load-stressed mast and boom members and electrically controllable means for actuating a plurality of forward and reverse movements of a load suspended from said boom member, in combination,

(a) a first member disposed in spaced adjacent relation to one of said stressed members and having one end portion fixed to said stressed member,

(b) switching means mounted upon the free end of said first member and electrically connected in series with the means for actuating forward movements of said load and in parallel with the means for actuating reverse movements of said load,

(c) a second member fixed to said stressed member and in spaced overlapping relation to said switching means and actuating the latter upon a predetermined deflection of said stressed member to interrupt electrical circuits in series with said switching means.

2. The device defined in claim 1, wherein said first and second members and said switching means are enclosed by a cover member detachably mounted upon said stressed member.

3. The device as defined in claim El, wherein said switching means comprises a plurality of microswitches, there being one said microswitch in series with the means for actuating each of the forward movements of said load.

4. In a material handling apparatus of the type described having load-stressed mast and boom members and electrically controllable means for actuating a plurality of forward and reverse movements of a load suspended from said boom member, in combination,

(a) a first member disposed in spaced adjacent relation to one of said stressed members and having one end portion fixed to said stressed member, said first member having a bifurcated free end portion,

(b) a third member connected to said first member and disposed Within said bifurcation and extending outwardly therefrom,

(0) switching means mounted upon the outwardly extending portion of said third member and electrically connected in series with the means for actuating forward movements of the load and in parallel with the means for actuating reverse movements of the load,

(d) a second member fixed to said stressed member and in spaced overlapping relation to said switching means and actuating the latter upon a predetermined deflection of said stressed member to interrupt electrical circuits in series with said switching means.

5. The device as defined in claim 4, wherein,

(a) said third member is pivotally connected intermediate its ends to the bifurcated end of said first member,

(b) said third member has a bifurcated inner end portion, and

(c) adjustable means at the inner end of said third 6 member biasing its pivotal movement relative to said first and second members, comprising,

(1) means connecting the confronting sides of the bifurcations of said third member, (2) a screwthreaded member passing through said first member and said connecting means, and (3) a spring around said screwthreaded member and emplaced between said connecting means and said first member.

6. The device as defined in claim 4,.wherein said second member has adjustable means thereon for actuating said switching means, comprising set screws mounted upon said second member and vertically disposed over said switching means in selectively spaced relation thereto.

7. In a material handling apparatus of the type described having load-stressed mast and boom members and electrically controllable means for actuating a plurality of forward and reverse movements of a load suspended from said boom member, in combination,

(a) a first member disposed in spaced adjacent relation to one of said stressed members and having one end portion fixed to said stressed member,

(b) switching means mounted upon the free end of said first member and electrically connected in series with the means for actuating all movements of the load and in parallel with an override switch, the latter being also in series with said means of actuating all movements of the load, and

(c) a second member fixed to said stressed member and in spaced overlapping relation to said switching means and actuating the latter upon a predetermined deflection of said stressed member to interrupt electrical circuits in series with said switching means.

8. In a material handling apparatus of the type described having load-stressed mast and boom members and electrically controllable means for actuating a plurality of forward and reverse movements of a load suspended from said boom member, in combination,

(a) a first member disposed in spaced adjacent relation to one of said stressed members and having one end portion fixed thereto,

(b) switching means mounted on said stressed member adjacent the free end of said first member, said switching means being electrically connected in series with means for actuating movements of said load and being actuated by said first member upon deflection of said stresed member to interrupt electrical circuits in series with said switching means.

References Cited by the Examiner UNITED STATES PATENTS 646,067 3/00 Colas 73-100 X 1,433,079 10/22 Jett. 2,731,198 1/56 Hathaway 235184 X 2,923,379 2/60 Stelzer 187 28 X 3,035,712 5/62 Nowack 2l239 SAMUEL F. COLEMAN, Primary Examiner. 

1. IN A MATERIAL HANDLING APPARATUS OF THE TYPE DESCRIBED HAVING LOAD-STRESSED MAST AND BOOM MEMBERS AND ELECTRICALLY CONTROLLABLE MEANS FOR ACTUATING A PLURALITY OF FORWARD AND REVERSE MOVEMENTS OF A LOAD SUSPENDED FROM SAID BOOM MEMBER, IN COMBINATION, (A) A FIRST MEMBER DISPOSED IN SPACED ADJACENT RELATION TO ONE OF SAID STRESSED MEMBERS AND HAVING ONE END PORTION FIXED TO SAID STRESSED MEMBER, (B) SWITCHING MEANS MOUNTED UPON THE FREE END OF SAID FIRST MEMBER AND ELECTRICALLY CONNECTED IN SERIES WITH THE MEANS FOR ACTUATING FORWARD MOVEMENT OF SAID LOAD AND IN PARALLEL WITH THE MEANS FOR ACTUATING REVERSE MOVEMENTS OF SAID LOAD, 